text: from gym.envs.mujoco import mujoco_env
  from gym import utils
  import numpy as np
  
  
  class HumanoidStandupEnv(mujoco_env.MujocoEnv, utils.EzPickle):
      def __init__(self):
          mujoco_env.MujocoEnv.__init__(self, "humanoidstandup.xml", 5)
          utils.EzPickle.__init__(self)
  
      def _get_obs(self):
          data = self.sim.data
          return np.concatenate(
              [
                  data.qpos.flat[2:],
                  data.qvel.flat,
                  data.cinert.flat,
                  data.cvel.flat,
                  data.qfrc_actuator.flat,
                  data.cfrc_ext.flat,
              ]
          )
  
      def step(self, a):
          self.do_simulation(a, self.frame_skip)
          pos_after = self.sim.data.qpos[2]
          data = self.sim.data
          uph_cost = (pos_after - 0) / self.model.opt.timestep
  
          quad_ctrl_cost = 0.1 * np.square(data.ctrl).sum()
          quad_impact_cost = 0.5e-6 * np.square(data.cfrc_ext).sum()
          quad_impact_cost = min(quad_impact_cost, 10)
          reward = uph_cost - quad_ctrl_cost - quad_impact_cost + 1
  
          done = bool(False)
          return (
              self._get_obs(),
              reward,
              done,
              dict(
                  reward_linup=uph_cost,
                  reward_quadctrl=-quad_ctrl_cost,
                  reward_impact=-quad_impact_cost,
              ),
          )
  
      def reset_model(self):
          c = 0.01
          self.set_state(
              self.init_qpos + self.np_random.uniform(low=-c, high=c, size=self.model.nq),
              self.init_qvel
              + self.np_random.uniform(
                  low=-c,
                  high=c,
                  size=self.model.nv,
              ),
          )
          return self._get_obs()
  
      def viewer_setup(self):
          self.viewer.cam.trackbodyid = 1
          self.viewer.cam.distance = self.model.stat.extent * 1.0
          self.viewer.cam.lookat[2] = 0.8925
          self.viewer.cam.elevation = -20